Ink jet printing is a process whereby a stream of ink, preferably in the form of droplets, is propelled against a medium so as to create an imagewise pattern, and while the present invention may be utilized in any recording medium of the type which imbibes a fluid ink, the primary utility of the present invention is in the production of ink jet recording media; and accordingly, will be explained primarily in that context.
Media used for ink jet recording must be dimensionally stable, absorptive of ink, capable of providing a fixed image, and compatible with imaging materials and hardware. In many instances, ink jet printing is carried out on simple paper media, particularly in those instances where correspondence and the like is being reproduced. However, certain applications will require that ink jet printing be carried out on a medium having a transparent base. Such applications include the production of backlit graphic displays, decals, posters and banners.
Particular problems arise when ink jet imaging is carried out on transparent media, and these problems are further enhanced when backlit images are produced. The typical inks employed in ink jet processes have a fairly high solvent content, and the solvents generally include high boiling, slow drying, relatively polar materials such as glycols, glycol ethers and water. The presence of fairly large amounts of relatively high boiling solvents in the medium can result in the production of an image having a tacky and/or greasy feeling surface. As a result, problems of blocking, smearing and image spread can occur.
One approach to these problems is detailed in U.S. Pat. No. 5,374,475, wherein an ink jet imaging medium is disclosed, which has an outer surface comprised of a non-ink-absorbing layer of material having a plurality of capillary passages defined therethrough which communicate with an ink receptive layer. An analogous approach is taken in patents 4,785,313 and 4,481,244 wherein a top, preferably porous, low absorbency layer is used to convey ink to a receptor layer therebeneath. Another approach is disclosed in U.S. Pat. No. 5,190,805, which shows an imaging medium which includes a hydrogel comprised of a complex of a comb graft copolymer together with relatively large amounts of a water soluble polymer. The hydrogel functions as an image receptor and requires the presence of significant amounts of pigment therein in order to enhance drying of the ink, and to limit lateral image diffusion. In some instances, a top coat may be present, provided it is fabricated from a material having an ink absorbtivity greater than that of the hydrogel.
In contrast, the present invention, is directed to an imaging medium having an image receptor layer on the top surface thereof, and a high absorbtivity, solvent imbibing layer therebeneath. The present invention provides an imaging medium which is durable, stable and receptive to a variety of inks including pigment based inks as well as dye based inks. The medium of the present invention provides a dry to the touch image which does not smear, block or spread. These and other advantages of the present invention will be apparent from the drawings, discussion, description and examples which follow.